This invention relates to coating compositions comprising polyarylates, the methods of preparing polyarylates and coated articles prepared using the coating compositions of the present invention.
Modern commerce and technology frequently employ organic coatings to shield various sensitive substrates from the harmful effects of the environment. Many such coatings are limited by long-term color instability, a limitation which is evidenced by a yellowing of the organic coating over time. Yellowing due to a coating's constituent polymeric components may be caused by the action of ultraviolet (UV) radiation. Another frequently encountered problem with organic coatings based on polymeric materials is poor resistance of the coating to chemicals and solvents after its application. Coatings which are tough, chemically resistant and “weatherable” (i.e. resistant to the effects of sunlight and other environmental conditions) are highly prized and diligently sought after.
Generally it has been observed that there is a tradeoff between weatherability and toughness in the performance of the commercial coating compositions known in the art. One solution to this problem has been the combination of extremely tough epoxies with polyesters to provide coatings with improved weatherability. Similarly acrylates, which are known to exhibit good weatherabiliy, but poor toughness, have been combined with polyester resins to improve their toughness. Compositions containing polyoxymethylene resins and various additives to improve toughness or impact strength are also known.
Certain types of polyarylates, known for their good weatherability and chemical resistance, have been found in the instant invention to be useful in the preparation of novel coating compositions having excellent scratch resistance and other properties. Up to the present, hydroxy-terminated polyarylates units have been prepared via interfacial polymerization methods. Despite recent strides in interfacial polyarylate synthesis, such interfacial methods are limited by an inability to control the molecular weight of the growing polyarylate chains. Typically the interfacial polymerization method provides polyarylates with high molecular weights, materials which may not be suitable for certain coating applications.
It remains of interest therefore, to develop coating compositions that demonstrate scratch resistance, toughness, chemical resistance and weatherability, suitable for application over various types of substrates in a wide variety of applications. There is also a need for synthetic methodology to prepare polymers comprising resorcinol chain members, having controlled molecular weight. The instant invention addresses these and other challenges and provides new and highly efficient solutions to them.